This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for CATHODE RAY TUBE HAVING MEANS FOR PREVENTING MIS-LANDING OF ELECTRON BEAMS BY EARTH MAGNETISM earlier filed in the Korean Industrial Property Office on May 18, 2001 and there duly assigned Serial No. 2001-27250.
1. Technical Field
The present invention relates to a cathode ray tube (CRT), and more particularly, to a cathode ray tube with a structure for preventing electron beam mis-landing caused by geomagnetism.
2. Related Art
Generally, a CRT is designed to realize an image by scanning a phosphor screen deposited with red R, green G, and blue B phosphors with electron-beams emitted from an electron gun.
The electron beams are deflected by a deflection yoke and landed on desired phosphors to scan the peripheral portion of the phosphor screen as well as the central portion.
However, when the electron beams are deflected, they are affected by outer magnetic fields such as geomagnetism, and the electron beams can be landed on an undesired phosphor. This so-called mis-landing deteriorates the color purity of the cathode ray tube.
To solve the above problem, a magnetic field shield member such as an inner shield for shielding the electron beams from geomagnetism has been employed in the CRT. The inner shield is generally mounted on a color selection apparatus composed of a shadow mask and a mask frame, which is disposed inside the cathode ray tube.
In recent years, a flat screen panel has been developed to improve the definition of an image realized at a peripheral portion of the large-sized screen. Accordingly, the color selection apparatus employed to realize colors in the CRT has been also flattened and increased in size so that it can be properly associated with the flat screen panel.
That is, a color selection apparatus includes a shadow mask provided with plural electron-beam-passing apertures and a frame for supporting the shadow mask applied with a predetermined tension. The frame includes a pair of elastic members and a pair of supporting members coupled to the elastic members, the shadow mask being mounted on the supporting members.
Such a color selection apparatus is mounted inside a panel on an inner surface of which a phosphor screen is formed. An inner shield is mounted on the supporting members and the elastic members such that it encloses electron beam emission traces to shield the electron beams from the geomagnetism.
Geomagnetism includes a vertical component and a horizontal component. The horizontal component can be classified as a north-south direction component (N-S component) that is in parallel with a tube axis, and an east-west direction component (E-W component) that is perpendicular to the tube axis. In the related art, to shield the electron beams from the horizontal component, a V-shaped notch or a piercing portion is formed on the inner shield.
However, the color selection apparatus still has a weakness against the E-W component of the geomagnetism.
That is, the E-W component is applied to lateral sides of the panel in a longitudinal direction. Therefore, since a space between the elastic members and the shadow mask and a space between the shadow mask and the phosphor screen are not shielded from the inner shield, the electron beams passing through these spaces are affected by the E-W component. This causes the electron beams to land on undesired phosphors, deteriorating the color purity of the cathode ray tube.
To solve the above problems, Japanese unexamined patent application having publication number No. H10-50228 for a Color Cathode-ray Tube by Teruhisa discloses a color cathode ray tube having shielding means for shielding the electron beams from outer magnetic fields applied between the color selection apparatus and the phosphor screen at the corners of the frame. However, since the shielding means is designed to enclose the corners of the frame, the amount of horizontal shift of the electron beams may be increased.
That is, when the shielding means is designed to cover the corners of the frame, the part of geomagnetism applied to the lateral sides of the frame flows into the longitudinal sides. Accordingly, the electron beams directed toward the corners are affected by the geomagnetism, and as a result, the amount of horizontal shift of the electron beams is increased. This causes the electron beams to land on undesired phosphors, deteriorating the color purity at the corners of the screen of the cathode ray tube.
Therefore, the present invention has been made in an effort to solve the above-described and other problems.
It is therefore an objective of the present invention to provide a cathode ray tube that is designed to minimize the effect on the electron beams by the geomagnetism, thereby improving the color purity of the cathode ray tube by enhancing the beam-landing accuracy.
It is another objective to provide a cathode ray tube that is designed to minimize the effect on the electron beams by geomagnetism and yet be easy and cost efficient to manufacture.
It is still another objective to provide an apparatus in a cathode ray tube that is designed to minimize the effect on the electron beams by geomagnetism while avoiding to affect the electrons beams in any other manner by the apparatus.
To achieve the above and other objectives, the present invention provides a cathode ray tube, including a panel having a front screen portion on which a phosphor screen is formed and a panel flange formed on an edge of the front screen portion; a funnel connected to the panel flange; a deflection yoke disposed around the funnel; a neck connected to the funnel; an electron gun disposed in the neck; a color selection apparatus for selecting electron beams emitted from the electron gun and allowing the selected electron beams to land on corresponding phosphors, the color selection apparatus including a frame having a pair of supporting members disposed at a predetermined distance from each other in parallel and a pair of elastic members fixed on both ends of the supporting members to correspond to lateral sides of the mask; and a shield apparatus for shielding geomagnetism, the shield apparatus being mounted on a perimeter of the frame of the color selection apparatus and extended toward the neck, wherein the shield apparatus includes disconnection parts defined corresponding to corners of the frame, the shield apparatus being extended toward the phosphor screen over one of longitudinal and lateral sidewalls of the frame.
According to an embodiment, the shield apparatus includes a main shield member having a body provided with an electron beam-passing opening and extended toward the neck, and a skirt extended from the body and disposed on longitudinal sides of the frame; and a sub-shielding member disposed on lateral sides of the frame.
Preferably, the skirt is fixed on the supporting members while covering a center of the supporting members. The skirt is formed to be asymmetrical with reference to a central portion of the supporting members.
Preferably, the main shield member is mounted on the frame while not enclosing the elastic members, and the sub-shield member includes a shielding part disposed along the lateral sides of the frame to cover a space defined between the mask and the elastic members; and coupling parts extended from the shielding part and fixed on the elastic members.
Preferably, a width of the shielding part is greater than that of the frame.
Further, preferably the skirt is connected to the supporting members while satisfying the following condition:
0.01 mmxe2x89xa6tk/Lxe2x89xa60.15 mm
where t is a thickness of the sub-shield member, k is a length of the skirt extending from the mask toward the phosphor screen over the supporting member, and L is a height of the supporting member.
Further, preferably the sub-shield member is fixed on the supporting member under the following condition:
0.01 mmxe2x89xa6txe2x80x2kxe2x80x2/Lxe2x89xa60.15 mm
where txe2x80x2 is a thickness of the sub-shield member, kxe2x80x2 is a length of the sub-shield member from the mask toward the phosphor screen, and Lxe2x80x2 is a height of the supporting member.